The goal for this project is to define the role of the lymphatic system in maintaining normal fluid balance in the liver, intestine and abdominal space of sheep. This is important because, in many human diseases, excess fluid may accumulate within the liver and intestine. Some of the excess fluid may flow into the abdominal space and cause ascites. However, the lymphatic system may prevent the excess fluid accumulation because lymphatic vessels drain fluid from the liver, intestine and abdominal space and transport the fluid to veins within the neck. Thus the lymphatics must pump fluid against the blood pressure in the neck veins. Accordingly, the elevated venous pressure which occurs in many human diseases could slow lymph flow. The first specific aim is to test the hypothesis that active pumping (pumping due to contraction of lymphatic vessel smooth muscle) in postnodal lymphatics helps to drive intestinal lymph flow. This will be done by comparing the flow vs. pressure relationships of intestinal lymphatics cannulated 1) directly at a node and 2) several centimeters downstream of a node. The second aim is to determine the effect of elevated neck vein pressure on fluid accumulation in the intestine and abdominal space. The third specific aim concerns the hypothesis that decreased lymphatic flow will cause decreased fluid absorption from the intestines. This will be tested by estimating the fluid absorption rate in control sheep and in sheep with decreased intestinal lymph flow. The results of all these studies should provide important information about the role of the lymphatic system in maintaining normal fluid balance in the liver, intestine and abdominal space.